Catalysts consisting of a zirconium compound and aluminoxane are known to exhibit a high polymerization activity in the polymerization of olefins, such as .alpha.-olefins (Japanese Patent Application Laid-open (kokai) No. 19309/1983). This method has a drawback in that a sufficient activity cannot be obtained unless expensive aluminoxane is used at a high ratio for a transition metal compound. In addition, not only preparing aluminoxane involves danger because of use of highly reactive trimethylaluminum to be reacted with water, but also its isolation from the reaction product as a single substance is difficult. Thus, controlling the catalyst for preparing a product with a stable quality has been difficult.
A method of using a homogeneous polymerization catalyst containing a reaction product of a transition metal compound, a coordination complex compound, and an organo-aluminum compound, as a major component, has been disclosed (Japanese Patent Application Laid-open (kokai) No. 207704/1991). As the coordination complex compound, a compound which can form an ionic complex by the reaction with a transition metal compound is used. Tetrakisphenylborate compounds are known as typical compounds among such coordination complex compounds.
This homogeneous catalyst containing the reaction product of such a tetrakisphenylborate complex compound and a transition metal compound as a major component is economical, because it requires no use of or only a small amount of expensive components such as aluminoxane. In addition, this catalyst can efficiently produce polymers having various characteristics. Because of these reasons, its active use as a catalyst for the polymerization of olefins, such as .alpha.-olefins and styrene monomers, is recently ongoing.
As raw materials for the synthesis of said tetrakisphenylborate complex compounds, tetrakisphenylborates, for example, lithium(pentafluorophenyl)borate [Li[B(C.sub.6 F.sub.5).sub.4 ]], can be used. A process according to the following reaction formulas is known as a process for preparing these tetrakisphenylborates [J. Organometal Chem., 2, 245-250 (1964)].
BrC.sub.6 F.sub.5 +n-BuLi.fwdarw.LiC.sub.6 F.sub.5 (in pentane, -78.degree. C.) PA1 3LiC.sub.6 F.sub.5 +BCl.sub.3 .fwdarw.B(C.sub.6 F.sub.5).sub.3 (in pentane, -78.degree. C.) PA1 B(C.sub.6 F.sub.5).sub.3 +LiC.sub.6 F.sub.5 .fwdarw.Li[B(C.sub.6 F.sub.5).sub.4 ] (in pentane, -78.degree. C.) PA1 BrC.sub.6 F.sub.5 +n-BuLi .fwdarw.LiC.sub.6 F.sub.5 (in ether, -78.degree. C.) PA1 4LiC.sub.6 F.sub.5 +BCl.sub.3 .fwdarw.Li[B(C.sub.6 F.sub.5).sub.4 ] (in ether, -78.degree. C.)
This process has drawbacks in that a complicated procedure is required for the synthesis of the final product, Li[B(C.sub.6 F.sub.5).sub.4 ], after isolation of the intermediate product, B(C.sub.6 F.sub.5).sub.3, and further that the reaction is delayed and the yield is reduced due to the reaction which takes place between solid LiC.sub.6 F.sub.5, which is produced by the use of pentane as a solvent, and liquid BCl.sub.3.
Another process, in which the reaction proceeds according to the following formulas, has been reported [Report from Asahi Glass Co., Ltd., Industrial Technology Motivation Institution, 42, 137 (1983)].
However, this process has a drawback of a low yield because of the use of ether as a solvent with which BCl.sub.3 produces a complex, which is insoluble in ether.